Filters with a high degree of separation encounter problems with pressure drop over the filter when used in a damp environment. In order to achieve the high degree of separation, the filters typically have very small passage openings. These openings also stop very small water drops. The openings get clogged by the water due to the surface tension and adhesion of the water to the filter material. Water in the form of fog, rain or condensation will in this way block many of the flow passages through the filter, at which the reduced available flow area increases the filter pressure drop. The increased filter pressure drop increases power losses in the filter. The removal of the water is preferable in many cases over having to increase the filter area as compensation at installations particularly since larger filters mean a big increase in cost. Even if one chooses not to increase the filter area, an energy loss is obtained as a result of the increased pressure drop. This energy loss can be considerable.
The present invention has as its object to remedy the above problem and provide a filter that is not influenced or at least only to a small amount by the pressure drop caused by moisture in the air that is to be filtered. Examples of filters where these phenomena may arise are the inlet filter to gas turbines used for power supply at oil platforms, as well as of course other filters that are used on oil platforms, boats etc.